Rabbit Rabbit 4000, User Manual

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Chapter 2 Clocks 11
2.2 Dependencies
2.2.1 I/O Pins
The main clock input is on the CLKI pin. There is an internal Schmitt trigger on this pin to
remove problems with noise on slowly-transitioning signals.
The main clock disable output is on the CLKIEN pin. Its state is changed by one of the bit
combinations of bits 4:2 in GCSR.
The 32 kHz clock input is on the CLK32K pin. There is an internal Schmitt trigger on this
pin as well.
The peripheral clock or peripheral clock divided by 2 may be optionally output on the CLK
pin by enabling it via bits 7:6 in GOCR.
The Ethernet clock may be input on pin PE6 by enabling it via bits 7:6 in NACR. It may be
set to use the processor clock or processor clock divided by 2 in that register as well. Note
that there is not an internal Schmitt trigger on PE6; it is highly recommended that an exter-
nal Schmitt trigger be placed on this pin if it is to be used as the Ethernet clock.
2.2.2 Other Registers
Register Function
GOCR Used to set up the CLK output pin.
NACR Used to set up the Ethernet clock.